Many electrical instruments such as, for example, optical measurement instruments and electrical instruments for cutting off sample regions from a sample carrier comprise one or more switch devices for controlling operation. A device for cutting off sample regions from a sample carrier is commonly used in a practice where one or more drops of fluid to be examined are impregnated onto a sample carrier, the sample carrier impregnated with the fluid is dried, and then the sample carrier is sent to a laboratory for analysis. The fluid to be examined can be, for example, blood of a newborn baby and the sample carrier can be, for example, a sheet of filter paper or some other suitable porous material which is able to absorb the fluid to be examined. In the laboratory, one or more sample regions containing the fluid to be examined are cut off from the sample carrier and the detached sample regions are conveyed, for further analysis, to sample wells of e.g. a microtitration plate or some other sample well element. Each sample region can be cut off from the sample carrier for example with a punch arranged to cut off the sample region with a single stroke through the sample carrier. In this case, the electrical instrument for cutting off sample regions from a sample carrier is typically called a puncher. It is also possible that the electrical instrument comprises cutting means, e.g. a laser or a water jet cutter, capable of producing a localized, point-form cut on the sample carrier and means for moving the point-form cutting impact produced by the cutting means along the outer periphery of each sample region so as to detach the sample region from the sample carrier.
An optical measurement instrument is applicable in cases where an analysis of a sample can be based on optical radiation emitted by the sample and/or on optical properties, e.g. an optical filtering effect, of the sample. One exemplifying analysis method is based on photoluminescence measurement where emission of a substance is measured from a sample with simultaneous excitation by illumination. Another exemplifying analysis method is based on chemiluminescence measurement where emission of a substance is measured from a sample without simultaneous excitation by illumination. An optical measurement instrument comprises typically an excitation light source for producing an excitation beam to a sample to be measured and a detector for detecting a beam from a sample being measured and for producing a detection signal responsive to the detected beam.
In the activity of the kind described above, cleanliness is very important. Thus, especially parts of a user interface of an electrical instrument which are touched during normal operation should be easy to keep clean. For example, switch devices for controlling an electrical instrument may comprise parts, for example push buttons, which are movable relative to their surroundings and thus there can be slits between these parts and their surrounding structures. In some cases, it may be laborious to keep such parts clean because dust and other impurities tend to gather into the slits. In a known technical solution, a user interface comprises a flexible sheet which covers the parts of the user interface which are touched during normal operation. The flexible sheet provides a uniform surface which does not have any slits and thus is easy to keep clean. The flexible sheet, however, increases the number of components and thus decreases the cost efficiency. Furthermore, the edges of the flexible sheet need to be joined to other structures of an electrical instrument so that the edges do not, in turn, form structures which may be difficult to keep clean.